Single Amino Acid Derived Rudimentary Catalytic Hydrogel for Reaction Engineering

Despite being structurally rudimentary, single amino acids and their derivatives demonstrate a remarkable ability to self-assemble into ordered nanostructures that renders potential catalytic activity. While many reports of catalysis utilizing amyloid-inspired peptide nanostructures are available, single amino acid derived hydrogel-based catalysts are rare. Herein, we report an elementary amino acid derivative, fluorenylmethoxycarbonyl-L-tryptophan (FT), based hydrogel that catalyzed the hydrolysis of p-nitrophenyl acetate, courtesy of the suitable positioning of indole residues in its ordered nanostructures. Exhibiting pathway complexity, the hydrogel nanofibers, initially formed as a kinetically trapped phase, underwent a morphological transition into thermodynamically stable semicrystalline microstructures, displaying better catalytic prowess than the hydrogel. Composite hydrogels with carbon nanomaterials improved the FT gels' mechanical properties and catalytic efficiency, ultimately bestowing enzyme-like hydrolytic activity. The FT hydrogel was finally utilized to engineer nanohybrid gels with gold nanoparticles as an efficient catalyst for dye degradation. The handling scope of these nanohybrid gels, along with morphological control, was improved by preparing core-shell hydrogel beads with alginate, realizing their practical catalytic potential for water remediation. Strikingly, a single hydrogel bead was capable of driving almost complete degradation for both cationic and anionic dyes. This reflects the optimized microenvironment for electron transfer and substrate diffusion within the porous structure of the developed beads. The efficacious catalysis by the bulk hydrogels/beads demonstrates the role of confinement, high surface area, and substrate diffusion through their porous architecture. Moreover, the hydrogels' semisolid nature offered excellent reusability, underscoring their role in sustainable and cost-effective catalytic applications.